The present invention relates to an electrical signal filter with an improved isolation shield for magnetically isolating electrically interconnected filter sections from one another. The present invention also relates to a modular electrical signal filter and filter assembly whose component parts can be assembled without the use of solder.
Various types of electrical signal filters are used in the CATV industry for controlling, on a frequency basis, the propagation of signals through a cable line. One example of such a filter is disclosed in U.S. Pat. No. 4,451,803, the entirety of which is incorporated herein by reference. The ""803 patent discloses a split tuning filter of the type that is commonly referred to as a notch filter, for removing a selected frequency or band of frequencies from a CATV signal. With reference to FIG. 7, the split tuning filter includes a common circuit board 100 having first 102 and second 103 filter sections formed thereon by discrete electronic components such as inductors, capacitors and the like (not shown). Isolation shields 104, 105 are arranged at a midpoint along circuit board 100 to provide magnetic isolation between first filter section 102 and second filter section 103. Each shield includes a radially extending disc section 106 and a longitudinally extending flange section 107. A slot 108 is formed in each shield, to allow the remaining, unslotted portion of disc 106 to slide into a corresponding slot 101 formed in circuit board 100. One of the shields is pressed into a slot formed on one side of the circuit board, and the other shield is pressed into a slot formed on an opposed side of the circuit board, as shown in FIG. 7. As explained in the ""803 patent, this arrangement prevents any xe2x80x9cline of sightxe2x80x9d communication between components in the first and second filter sections.
Once the shields 104, 105 are positioned on opposite sides of circuit board 100, the circuit board is inserted into housing 109, the open end of which is closed by filter cap 110. This subassembly is then inserted into a tube sleeve housing (not shown) to form the final sealed filter structure.
While the filter disclosed in the ""803 patent is highly successful in providing magnetic isolation between the first 102 and second 103 filter sections, there are several drawbacks associated with the use of shields 104 and 105. First, the shields must be soldered not only to circuit board 100, but also to filter housing 109, in order to ground the circuit board. While the shields can be soldered to circuit board 100 with relative ease, it is relatively difficult to solder the shields to filter housing 109 once the shields are positioned within the confines of the housing. In order to achieve this type of soldering operation, it is necessary to apply a high heat source to the exterior of filter housing 109, which can adversely effect the characteristics of the electrical components already positioned on circuit board 100. It is also difficult to control the flow of solder within the confines of filter housing 109, and thus it is not uncommon for one or both sides of the filter to become shorted. Such shorted filters must, of course, be discarded.
Another problem relates to flange 107. The flange is present on each shield in order to guide circuit board 100 into filter housing 109 and to provide a soldering surface parallel to the wall of filter housing 109. The electronic components on the circuit board, however, must be spaced away from the shields by a distance greater than the longitudinal length of flange 107 to allow the shields to be inserted into slots 101 on opposite sides of circuit board 100. The longitudinal length of flange 107, therefore, unnecessarily increases the overall length of the filter. This problem is even more noticeable in six-pole and eight-pole filters, which use multiple shields.
Yet another problem is that the shields, being separate components, increase the total number of components that must be handled during assembly of the overall filter device. This in turn increases manufacturing time and expense.
Yet another problem with the prior art filter shown in FIG. 7 is that the end cap 110 must be soldered to the filter housing 109 in order to prevent rotation of the end cap 110 independent of the filter housing 109. Since the filter is rotatably installed as a unit, it is unacceptable if one part of the filter is able to rotate independent of other parts of the filter. This necessary soldering step adds expense to the overall filter assembly. Although electronic components of the circuit board 100 are soldered in place, that soldering step can be performed in a very efficient, mass-production scale prior to assembly of the filter components into the final filter product.
In order to ensure a good ground contact between the circuit board 100, the shields 104 and 105, and the housing 109, it is also necessary to solder the shields to the board to the housing during assembly of the filter. This soldering step also adds expense to filter assembly, and can be quite difficult, since the shields are positioned inside the filter housing 109 during the soldering operation.
Another problem prevalent in the CATV filter industry is that each distinct filter application currently requires a distinctly accommodating filter housing. Given the vast number of different types of filter applications, it has become necessary to design, manufacture, and maintain sufficient inventories of each individual type of filter housing for each of the different filter application products offered. This can be particularly inconvenient and expensive for electronic signal filter providers that offer a wide variety of products for a wide variety of applications.
For example, providing the machinery and manpower required to machine a large number of different filter housings having different design specifications and considerations can be an expensive undertaking. Even when the filter housing is designed to be formed by casting rater than being produced using machining techniques, producing a large number of different filter housings nonetheless mandates the use of many different manufacturing molds.
Moreover, different filter housing configurations may require different manufacturing steps to complete the assembly of the final electronic signal product, depending on the structural design. As mentioned above, additional manufacturing processes, such as manual assembly or soldering steps, drive up the cost of the final products, introduce additional opportunities for quality control issues to arise, and further complicate the manufacturing process. Accordingly, the need to manage and control the varying specifications and requirements for production of varying design applications involves increased manpower and equipment required to monitor and ensure quality, which ultimately increases production costs. Additionally, the expenses associated with providing storage facilities and logistics support in the form of personnel, equipment and for complex inventory management are another cost aspect that increases the costs of the final filter products.
It would be desirable to provide an electrical signal filter having isolation shields that are easy to handle and solder within the filter housing. It would be more desirable to provide an electrical signal filter whose component parts can be assembled into the final filter product without any soldering steps. It would also be desirable to provide a xe2x80x9cuniversalxe2x80x9d modular filter housing that can be used for any filter application, either alone as a single modular unit or in combination with a plurality of other modular units. It would also be desirable to provide modular filter components that can be assembled into the desired filter assembly configurations without any soldering steps.
It is an object of the present invention to provide an electrical signal filter that can overcome all the drawbacks associated with the prior art filters discussed above. In accordance with one object of the present invention, an electrical signal filter is provided that includes an elongate lower filter housing member extending along a first longitudinal direction from a first end thereof to an opposed second end thereof, and having an inner surface terminating at first and second upper side surfaces that extend from the first end to the second end. The filter also includes an elongate upper filter housing member extending along the first longitudinal direction from a first end thereof to an opposed second end thereof, and having an inner surface terminating at first and second lower side surfaces that extend from the first end to the second end. The elongate upper filter housing member abuts the elongate lower filter housing member at the first and second lower and upper side surfaces, respectively, along a longitudinal junction. An isolation shield is formed integrally with at least the elongate lower filter housing member and extends inwardly and upwardly from the inner surface thereof in a direction substantially perpendicular to the first longitudinal direction to thereby define first and second internal filter cavities separated by the isolation shield. A first filter section is arranged in the first internal filter cavity and a second filter section, electrically connected to the first filter section, is arranged in the second internal filter cavity. The isolation shield provides magnetic isolation between the first and second filter sections.
In accordance with a preferred embodiment, the isolation shield extends inwardly and upwardly from the inner surface of the elongate lower filter housing member to a position proximate a plane intersecting the first and second upper side surfaces thereof, and a second isolation shield is formed integrally with the elongate upper filter housing member and extends inwardly and downwardly from the inner surface thereof in axial alignment with the isolation shield of the elongate lower filter housing member.
More preferably, the upper surface of the isolation shield of the elongate lower filter housing member has a shape that is complementary to a shape of the lower surface of the second isolation shield of the elongate upper filter housing member, and those surfaces mate with each other to form the appearance of an integral shield.
In accordance with another embodiment of the invention, an electrical signal filter is provided that includes an elongate lower filter housing member extending along a first longitudinal direction from a first end thereof to an opposed second end thereof, and having an inner surface terminating at first and second upper side surfaces that extend from the first end to the second end, and an elongate upper filter housing member extending along the first longitudinal direction from a first end thereof to an opposed second end thereof, and having an inner surface terminating at first and second lower side surfaces that extend from the first end to the second end. The elongate upper filter housing member abuts the elongate lower filter housing member at a junction between the first and second lower side surfaces and the first and second upper side surfaces, respectively, to thereby define an internal filter cavity. A ground post is formed integrally with the lower filter housing member and extends upwardly from the inner surface thereof in a direction substantially perpendicular to the first longitudinal direction. A circuit board is positioned within the filter cavity and has a ground terminal fastened to the ground post without the use of solder. First mechanical engagement members extend circumferentially around portions of the outer surface of each of the upper and lower filter housing members proximate the first and second ends thereof. End caps are positioned on the first and second ends of the abutted upper and lower filter housing members, and each of the end caps has a second mechanical engagement member formed on an inner surface thereof that is complementary to and mates with the first mechanical engagement members formed on the upper and lower filter housing members.
The structure of this embodiment allows for the omission of any soldering steps during assembly of the component parts of the filter, because a mechanical engagement is provided between the ground post of the lower filter housing member and the circuit board, and mechanical engagement members are also used for preventing rotation of the end caps to the abutted filter housing members. As a result, the overall cost of manufacturing the filter can be reduced.
According to another embodiment of the present invention, a modular filter housing assembly is provided, including a plurality of elongate filter housings. In particular, a first filter housing is included, extending in a longitudinal direction from a first end thereof to an opposed second end thereof and having a mechanical engagement member provided on at least one of the first and the second ends thereof. A second filter housing is also included, extending in the longitudinal direction from a first end thereof to an opposed second end thereof and having a mechanical engagement member provided on at least one of the first and the second ends thereof. Further, a coupling member is also included, having a first end provided with a corresponding mechanical engagement member to engage the mechanical engagement member provided on one of the first and the second ends of one of the first and the second filter housings and an opposed second end provided with a corresponding mechanical engagement member to engage the mechanical engagement member provided on one of the first and second ends of the other filter housing to join the first filter housing and the second filter housing to one another in a solderless connection via the coupling member.
Preferably, the mechanical engagement member of the first filter housing comprises an outer surface portion of the first end of the first filter housing having an outer diameter d1, and the mechanical engagement member of the second filter housing comprises an outer surface portion of the first end of the second filter housing having an outer diameter d2. Further, the first end of the coupling member comprises an inner surface having an inner diameter d3, and the second of the coupling member comprises an inner surface having an inner diameter d4. Preferably, inner diameter d3 is sufficiently less than outer diameter d1 to provide a secure mechanical press-fit between the first end of the first filter housing and the first end of the coupling member, and inner diameter d4 is sufficiently less than outer diameter d2 to provide a secure mechanical press-fit between the first end of the second filter housing and the second end of the coupling member.
The secure press-fit relationship between the filter housings and the coupling member eliminates the need to provide solder at this joining region, and thus reduces the required production materials (i.e. solder), reduces the number of manufacturing steps, and ultimately lowers the costs associated with producing an electrical filter assembly for any particular application.
The modularity achieved by the present invention also offers heretofore unrealized flexibility and convenience with respect to both manufacturing and logistics. That is, any desired filter application can be assembled using a xe2x80x9cuniversalxe2x80x9d modular filter housing that can be interconnected with any number of other like modular filter housings via a single type of coupling member to fulfill any particular application specification.
Thus, the filter housings and coupling members can be used for all filter application products offered by a particular entity and tailored to a particular product application as demanded. This eliminates the need to stock and manage a large number of different filter housings suited to accommodate all of the filter application products offered. This also streamlines the overall manufacturing process associated with filter housing production, since a single mold design or machining set-up can be used to produce all of the modular filter housing and coupling member units.
The mechanical engagement member of the first filter housing preferably extends circumferentially around at least a portion of an outer surface thereof proximate the first end thereof, and the mechanical engagement member of the second filter housing member extends circumferentially around at least a portion of an outer surface thereof proximate the first end thereof.
According to another embodiment of the present invention, each of the mechanical engagement members of the first and the second filter housing members include anti-rotational mechanisms, and each of the corresponding mechanical engagement members of the coupling member include corresponding anti-rotational mechanisms. Preferably, the anti-rotational mechanism of the first filter housing is one of a series of projected ribs and a series of grooves, and the corresponding anti-rotational mechanism of the first end of the coupling member is the other one of a series of projected ribs and a series of grooves. Similarly, the anti-rotational mechanism of the second filter housing is preferably one of a series of projected ribs and a series of grooves, and the corresponding anti-rotational mechanism of second end of the coupling member is preferably the other one of a series of projected ribs and a series of grooves.
The anti-rotational mechanism helps to maintain the structural integrity of the filter assembly by significantly reducing the degree to which the filter assembly experiences undesired longitudinal torque. That is, the interlocking anti-rotational mechanism substantially prevents the filter housings from rotating independently with respect to one another and with respect to the coupling member or members that interconnect the filter housings.
According to another embodiment of the present invention, the first filter housing also includes a mechanical engagement member formed on the second end thereof, and the second filter housing member further likewise includes a mechanical engagement member formed on the second end thereof. A plurality of end caps are also preferably provided. Each end cap preferably includes a corresponding mechanical engagement member provided on an inner surface thereof to engage a respective one of the mechanical engagement members provided on the second end of the first filter housing and the second end of the second filter housing.
The mechanical engagement members of the end caps also preferably include anti-rotational mechanisms that correspond to the anti-rotational mechanisms provided on the ends of the filter housing, as well. Preferably, the corresponding anti-rotational mechanisms of each end cap is the other one of a series of projected ribs and a series of grooves, depending upon which is provided on the corresponding second end of the respective filter housing members.
After the end caps are positioned on the ends of the filter housings, an outer protective tube is preferably secured over the end caps, the first and second filter housings, and the coupling member through interposed sealing members (e.g., O-rings). It should be noted, however, that according to another embodiment of the present invention, the aforementioned end caps can be integrally formed with the filter housings. In that manner, the casting and assembly process can be further simplified, as described in more detail below.
According to yet another embodiment of the present invention, each modular filter housing member includes a lower filter housing member and an abutted upper filter housing member that are solderlessly joined to one another in a vertical direction to form a split-housing member. Each end of each split housing member is connected to one of an end cap or a coupling member, essentially in the same manner as described above.
Again, the modularity afforded by the present invention allows the split housing members to be castably produced from a single mold or machined using a single machine set-up. Although the present invention preferably enables a single modular filter housing member design, or a like pair of modular split filter housing members, to be used for any filter application, it is also possible to assemble a wide variety of filter housing configurations for a wide variety of filter applications using only a few different upper and lower filter housing configurations that are able to accommodate different filter components. For example, filter components of varying heights, such as inductor coils, often call for filter housings having larger (or smaller) inner diameters. In that way, a very small number of different modular stock models could be used to tailor a filter for any desired application.